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PICTURED: The soon-to-launch SPHEREx space observatory. PC: Caltech.
Story at a glance…
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A telescope that will map the entire sky every six months has been funded and set for a 2024-2025 launch date.
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It will detect water-ice in the Milky Way and provide insight into inflation in the moment after the Big Bang.
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Instrument Scientists Phil Korngut from Caltech speaks to WaL about the project, set to perfectly complement the James Webb Telescope.
The launch of the James Webb Space Telescope in December 2021 was the culmination of three decades of Herculean efforts. However another cosmic mapmaker developed in Webb’s shadow is set to launch in the spring window of 2024 or 2025, and promises to be maybe even more important.
The “Spectro-Photometer for the History of the Universe, Epoch of Reionization and Ices Explorer,” is the mission’s official title, and is much better known as SPHEREx. This observatory will map the entire sky every six months, indiscriminately gathering data on 300 million galaxies, including the oldest ones in the sky.
In short SPHEREx will take a picture of the whole sky with enough detail to allow researchers to identify unique or important characteristics of a star, galaxy, or exoplanet, that can inform missions of targeted observatories like JWST or even Hubble.
“There’s definitely a complimentarity,” remarks Phil Korngut, Instrument Scientist at the California Technical Institute team that’s currently building the observatory. “They are very different beasts. The metaphor I like to use is a chainsaw and a scalpel are both ‘cutting implements’ but you use them for very different things”.
“With SPHEREX we’re going to survey everything and it’s much easier to find interesting objects this way, and then you know where to look with JWST”.
NASA originally chose to fund SPHEREx, costing around $243 million, in 2019, specifically because of its unparalleled ability to collect data and deposit it into the astronomical science community, which can then be used as the basis of research and follow up observations with flagship observatories like Hubble, JWST, or the future Wide Field Infrared Survey Telescope.
Martini on the rocks
Unlike the JWST which is hundreds of thousands of miles from Earth, the cone or tulip-shaped SPHEREx will be much closer to home, which deeply influenced the engineering.
“The ‘martini glass’ of nestled conical panels are photon shields,” Korngut explains to WaL. “SPHEREx lives in low-earth orbit, and when you’re working in the infrared [light spectrum] things that are warm are the enemy. They’re glowing in the near-infrared, so our telescope has to be cooled down to very low temperatures”.
“We have our telescope nestled in the three-stage photon shields and those block the radiation coming up from the earth and across from the sun. It’s super fun and exciting in that we’ve been designing this thing for the better part of a decade, and now we’re building it”.
Inside, the telescope will look, as Korngut explains, into the infrared. This wavelength of light is sometimes called heat radiation, but it isn’t visible to the human eye. If you want to see the earliest history of the universe, the infrared is necessary.
On top of that the telescope comes with an enormous field of view equipped with spectroscopy capabilities. Spectroscopy allows light to be broken down into individual wavelengths which appear like colors (think Pink Floyd’s Dark Side of the Moon). This will allow SPHEREx to reveal what an object is actually made of, because individual chemical elements absorb and radiate specific wavelengths of light.
A series of infrared-spectroscopic filters are put over the telescope’s detectors, and it in turns scans the skies relentlessly with every piece of the sky landing on every point of the focal plane that goes through every filter’s wavelength, thus creating a spectroscopic map of the entire sky every six months for two years.
After the first year, slight adjustments can be made to account for changes in the position of the observatory, and the process can start up again, providing at least two identical, potentially more, three-dimensional maps of the universe.
Back to the beginning
Like all NASA missions, SPHEREx will have primary science objectives. After it finishes its first survey, it will release bulk datasets out to the scientific community.
“We’re studying the large scale structure of the universe, and from that trying to make inferences from the very earliest epics of the universe in a period called ‘inflation,’” says Korngut.
“We’ve got our galaxy formation theme which studies by making statistical measurements to the background light field to put constraints on the history and evolution of galaxies, but also in our own neighborhood in the surveying of the galactic plane for biogenic ices like water-ice”.
One of the reasons it’s necessary to scan the entire sky, points out SPHEREx press officer Calla Cofield, is that the data this observatory will hopefully collect about the extremely early universe can only be contextually understood with a perspective that contains a massive chunk of it.
Recently the Hubble telescope published an image of the oldest star ever observed at some 28 billion light years away. A lot can be learned but such a discovery, but a lot more could be gleaned if the whole sky were imaged.
If two cars set out on in single file on the same trajectory, and one driver turns the steering wheel 1° to the left, some minutes would have to pass before the cars would lose sight of one another.
During the moments just after the Big Bang, tiny quantum fluctuations altered the path of ejecting matter such that over billions of years, like the two cars, those initial alterations massively changed the position of galaxies in the universe. Using mathematics, physicists and astronomers can calculate where some galaxies started and ended up in relationship to each other, but only if they have an image of the whole relationship, which Korngut describes as needing at least a 30° angled view of the sky.
With an April launch date in 2024-2025, it’s possible that by the end of the decade, a paper will be published detailing the procession of galaxies from the moment of the Big Bang, on to present day, one that includes the more-or-less exact position of every galaxy in the universe, and it will be all thanks to SPHEREx.
“There’s going to be some really cool stuff which comes out of [the survey data], and I don’t know what it is, but the ancillary data is truly powerful for anything that you’re trying to do statistics for,” Korngut hypothesizes, “but also for like, rare objects”.
“High red-shift quasars: I don’t know what the running count is, but I think it’s like three”.
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